Thermal Desorption Tubes

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Thermal Desorption Gas Chromatography Applications

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Overview

Thermal Desorption Introduction

Supelco products include a comprehensive selection of adsorbent tubes – Carbotrap™ tubes – offering superior performance for trapping and thermally desorbing organic compounds. Selection of the proper adsorbent(s) is critical to achieving the best results for a thermal desorption application. An ideal adsorbent tube will trap and retain compounds of interest for the entire sampling period, then allow total analyte desorption without thermal decomposition. The rate of release should be as rapid as possible, to minimize analysis time and provide the most efficient separation. Stable adsorbents ensure the best detection limits by minimizing the possibility of breakdown products interfering with quantification.

Multi-Bed Adsorbent Tubes

Because no single adsorbent is capable of trapping and efficiently releasing all compounds, many Carbotrap™ thermal desorption tubes contain more than one adsorbent. Multiple beds of adsorbents enable you to analyze a wider range of compounds in a single sampling. In multi-bed adsorbent tubes, the adsorbents are arranged in order of increasing adsorbent strength, from sample inlet to sample outlet. The largest molecules in the sample are trapped by the first bed of adsorbent. Smaller molecules are trapped by the succeeding, stronger beds. To avoid forcing analytes through an adsorbent that is too strong, desorption flow is always in the direction opposite of sample collection flow.

Tube Construction

The design of a thermal desorption tube and its contents are critical to a well-performing air monitoring system. Glass tube blanks are manufactured to close tolerances, to ensure consistent lot-to-lot performance. For identification, we mark each of our glass tubes with a unique number. Thermal desorption tubes are most commonly made of glass or stainless steel, with glass wool, wire gauze, or glass frits to hold the adsorbents in place. Tube lengths and outside diameters are dictated by the instrument of choice. Tubes having a large internal volume (4mm I.D. or greater) are typically used for sampling because they hold relatively large size beds of adsorbents. Analytical results can be improved by transferring the analytes from the large I.D. sampling tube to a tube of smaller I.D. (1-2mm), thus “focusing” the sample into a smaller volume. Subsequent desorption from the smaller I.D. tube to the chromatography column gives a higher linear velocity of desorption flow through the tube, delivering the sample to the column more rapidly and in a much narrower band.

Empty Tubes

We mark these specially cleaned and silanized glass tubes with an arrow to indicate sampling flow direction. Fill them in this direction with successively stronger adsorbents. You can fill an empty 4 mm I.D. tube with adsorbents for air sampling, or with a solid sample (soil, plastic, etc.) for a thermal extraction analysis. Use our empty 1 mm I.D. and 2 mm I.D. tubes to create your own focusing tubes, for better chromatography.

To trap highly sensitive compounds, use an adsorbent tube with a frit in the inlet rather than a glass wool plug. The frit will hold the adsorbent in place without adsorbing or decomposing the analytes; glass wool plugs can adsorb or degrade sensitive compounds.

Tubes by Instrument Manufacturer

Tubes for DANI, Markes, OI Analytical and Shimadzu Instruments

Supelco products include both stainless steel and glass-fritted pre-packed sampling tubes that are fully compatible with DANI, Markes, OI Analytical and Shimadzu thermal desorbers. Each glass-fritted tube is equipped with a ceramic unique number code-128 barcode. Each stainless steel tube features high quality tube markings and a unique number. The tubes are pre-conditioned, QA tested and ready for use with our exclusive TDS³ storage container. Also available sealed with brass endcap fittings.

Tubes for Teledyne Tekmar Instruments

Supelco products include glass and stainless steel tubes for Teledyne Tekmar instruments. Our prepacked tubes are thermally conditioned and tested for background levels and backpressure. The ¼ in. O.D. tubes are sealed in our exclusive TDS³™ storage container and the ½ in. O.D. tubes are sealed in a glass storage container. Fits AEROTrap 6000 instrument.

Tubes for Gerstel ThermoDesorption System 

Supelco products include stainless steel and glass pre-packed sampling tubes that are fully compatible with the Gerstel instrument. Each tube is thermally conditioned, and batch tested for backpressure and background. The pre-packed tubes are sealed in our exclusive TDS³™ storage containers. All of the pre-packed glass sampling tubes incorporate a glass frit at the inlet, which increases their performance, and are individually numbered. The stainless steel tubes use a SS screen at both inlet and outlet to keep the adsorbent beds secure during use. Each stainless steel tube includes two stainless steel screens.

Tubes for CDS/DYNATHERM Instruments

Supelco products include a complete line of both pre-packed and empty tubes for the DYNATHERM Thermal Desorbers. Each tube is individually numbered, thermally conditioned, and batch tested for backpressure and background. The pre-packed Standard Sampling Tubes are sealed in our exclusive TDS³™ storage containers and the Fast-Flow Tubes are sealed with Swagelok® fittings. All of the pre-packed sampling tubes incorporate a glass frit at the inlet, which increases their performance. The Focusing tubes are used to refocus the sample for better chromatography of the early eluting compounds.

VOST Stack Sampling Tubes

VOST (volatile organic sampling train) Tubes are designed to meet specifications in US EPA SW-846, Method 0030. Each tube is individually numbered, pre-conditioned, and sealed with stainless steel Swagelok^® fittings before stored in a glass storage container. Each lot is tested for background and backpressure.